1. Field of the Invention
The present invention generally relates to a fixing device used in an image forming apparatus such as a copier, a facsimile machine, a printer and the like. More particularly, the present invention relates to a fixing device and an image forming apparatus including the fixing device, the fixing device fixing resin particles onto a recording medium by applying a foam-like fixing material to the resin particles, the foam-like fixing material being capable of dissolving or swelling the resin particles including toner.
2. Description of the Related Art
It is known that image forming apparatuses such as a printer, a facsimile machine, a copier, an MFP (Multi-Function Peripheral) and the like form images including characters and symbols onto a recording medium such as a sheet, fibers, an OHP sheet and the like based on image information. Among the image forming apparatuses, an electrophotographic-type image forming apparatus has been widely used because a high-resolution image using resin-containing particles can be formed onto a regular paper. The resin-containing particles refer to particles containing resin as one of the components. Further, the toner refers to the resin-containing particles used in the electrophotographic-type image forming apparatus, and contains materials that can develop (express) necessary functions for the electrophotographic-type image forming apparatus, the materials including a charge controlling agent that develops the charging performance in the resin-containing particles, a color material that expresses a color, and a material that prevents the particles from being adhered to each other.
In such an electrophotographic-type image forming apparatus, the fixing speed is fast and the fixed image quality is high. Because of the features, a heat fixing method is widely used, where toner on the recording medium is heated to dissolve the toner and the dissolved toner is pressed to fix the toner onto the recording medium. The image forming apparatuses such as a printer, a facsimile machine, a copier, an MFP and the like using the heat fixing method form images including characters and symbols onto a recording medium such as a sheet, fibers, an OHP sheet and the like based on image information. Among the image forming apparatuses, an electrophotographic-type image forming apparatus has been widely used because a high-resolution image using resin-containing particles can be formed onto a regular paper.
In the electrophotographic-type image forming apparatuses, more than half of the energy supplied is consumed by heating toner. Therefore, it is not easy to greatly reduce the consumption of energy of such image forming apparatuses for energy conservation.
From the viewpoint of addressing recent environmental problems, it has been desired to provide a fixing device requiring less energy consumption (an energy-saving fixing device), which is namely, a fixing device using a non-heating fixing method in which toner is fixed without heating the toner.
As an example of the non-heating fixing method, there is a wet fixing method in which toner is softened by adhering an organic solvent capable of dissolving or swelling toner to the toner. For example, there is a known wet fixing method in which a fixing liquid is generated in a foam, and the generated foam-like fixing liquid is applied to resin particles on a recording medium while the film thickness of the generated foam-like fixing liquid is controlled to fix the resin particles onto the recording medium (see, for example, Japanese Patent No. 4302700, hereinafter “Patent Document 1”). Herein, the term “foam-like” generally refers to a foam state. However, according to a more strict expression, the term “foam-like” refers to a continuous body where plural air grains (air bubbles) surrounded by liquid films are integrated with the liquid films.
According to Patent Document 1, by making the fixing liquid into foam and applying the fixing liquid to a recording medium on which an image using resin-containing particles (hereinafter a unfixed toner image T) is formed, unfixed resin-containing particles can be fixed without being offset to the fixing material side or without disturbing the positions of the unfixed resin-containing particles. Further, the foam-like fixing material contains a large amount of air bubbles. Therefore, the volume of the fixing liquid is smaller than the volume of the foam-like fixing material. As a result, the amount of the liquid applied to the recording medium is reduced. Further, without causing a change when touching the recording medium and without undulating the recording sheet, it becomes possible to fix the image without degrading the fixing capability and the fixing quality.
The foam-like fixing material as described in Patent Document 1 is carried onto the surface of the application roller and then applied to a sheet. However, after being applied to the sheet, some of the foam-like fixing material may remain on the application roller. Further, besides the residue of the fixing material, for example, a part of toner, and paper powder that was on the sheet may also be adhered to the application roller. Because of this feature, it is preferable to clean the application roller before the next fixing material is applied to the surface of the application roller.
As a technique of cleaning the application roller, there is a technique in which the application roller is cleaned by bringing a cleaning blade into contact with the surface of the application roller. In this case, to enhance the cleaning performance, the cleaning blade is required to be in contact with the application roller in a manner such that the touching end of cleaning blade faces the moving direction of the application roller (i.e., in a so-called counter blade manner) which is the fixing material carrier.
On the other hand, though it is not a known technique to clean the application roller using the cleaning blade, there is a known technique to clean the toner and the paper powder adhered to a photosensitive body, the charging roller and the like using the cleaning blade. In this technique, while no image is being formed, by rotating the photosensitive body in the reverse direction, the toner and foreign particles remaining at the distal end of the cleaning blade are removed from the end of the blade (see, for example, Japanese Patent Application Publication No. 05-341624, hereinafter “Patent Document 2”).
Further, as the configuration to clean the photosensitive body, there is known another technique in which a non-volatile lubricant liquid is applied to a point on the surface of the photosensitive body, the point being disposed on the upstream side or the downstream side of the cleaning blade which is in contact with the photosensitive body (see, for example, Japanese Patent Application Publication No. 58-115468, hereinafter “Patent Document 3”).
However, in Patent Document 1, in a case where the cleaning blade is in contact with the application roller in the counter blade manner, if the frictional resistance to sliding the cleaning blade on the surface of the application roller is high, the contact edge of the cleaning blade may be bent (folded) by the rotation of the application roller, the contact edge being disposed closer to (or being in contact to) the application roller. When the contact edge of the cleaning blade is bent (folded) by the rotation of the application roller, the cleaning performance may be degraded.
In other words, in the fixing device using the foam-like fixing material, while the apparatus is continuously used, the surface of the application roller and the surface of the cleaning blade are sufficiently wetted by the foam-like fixing material, and therefore the frictional resistance to sliding the cleaning blade on the surface of the application roller is low. As a result, the contact edge of the cleaning blade may not be bent (folded) by the rotation of the application roller. However, when the apparatus is used intermittently, or just after the apparatus has started operating, due to dried fixing material or the adhesion of the paper powder and the like, there may be a case where the fixing material having viscosity higher than a normal value remains on the surface of the application roller. In such a case, the frictional resistance to sliding the cleaning blade on the surface of the application roller is high. As a result, when the application roller rotates in the direction so that the application roller collides with the cleaning blade, it may be more likely to bend (fold) the contact edge of the cleaning blade by the rotation of the application roller.
Further, the technique of Patent Document 2 is to remove foreign matter adhered to the cleaning blade after cleaning. More specifically, the technique is to remove foreign matter from the cleaning blade by rotating the photosensitive body or the like in the reverse direction, the foreign matter having been adhered during the image forming operations. Because of this feature, this technique cannot be applied to the cleaning blade and the application roller to prevent the bending (folding) of the contact edge of the cleaning blade due to the rotation of the application roller. Namely, in order to prevent the bending (folding) of the contact edge of the cleaning blade due to the rotation of the application roller, it is required to make the frictional resistance to sliding the cleaning blade on (against) the surface of the application roller sufficiently high. However, again, the technique of Patent Document 2 is to remove foreign matter from the cleaning blade by rotating the photosensitive body or the like in the reverse direction. Therefore, it is not feasible to apply the technique to the cleaning blade and the application roller to prevent the bending (folding) of the contact edge of the cleaning blade due to the rotation of the application roller.
Further, in the technique described in Patent Document 3, a non-volatile lubricant liquid is used. This feature is not preferable due to safety concerns.
On the other hand, in a case where water having an advantage in the safety point of view is used as a main component of the fixing liquid and the lubricant liquid, while the apparatus is stopped, water content of the fixing liquid and the lubricant liquid remaining on the fixing material carrier such as the application roller gradually vaporizes. As a result, the components other than water are condensed, which may impede (increase the frictional resistance of) the sliding of the cleaning blade on the application member (i.e., application roller). Further, solid content may be precipitated, which may cause adhesion between the cleaning blade and the fixing material carrier. Therefore, it is desirable to apply the lubricant agent just before the fixing is started.